Magnetic refrigeration is a cooling refrigeration technology based on the magnetocaloric effect.
The refrigerant capacity RC is a main figure of merit for characterizing the magnetocaloric response of any magnetic refrigerant since it measures the amount of heat that can be transferred from the cold to the hot sink during an ideal refrigeration cycle. In practice, a large refrigerant capacity depends on having a broad magnetic entropy change as function of the temperature curve, [ΔSM(T)].
Hence, any increase in the temperature that define the full-width at half-maximum of the curve results in an enhancement of RC.
Magnetic refrigeration is currently of interest since it both, more efficient from the energy point of view (up to a 30%) and environment-friendly in comparison with the conventional gas-based refrigeration; thus it is economically and environmentally convenient.
Some of the reported magnetocaloric materials such as MnAs and MnFeP0.45As0.55 with favourable magnetocaloric effect in a temperature range from 250 to 320 K (U.S. Pat. No. 7,069,729B2), contain toxic elements such as Arsenic which could be dangerous for domestic uses. K. A. Gschneider Jr. et al. (J. Appl. Physics, Vol. 85, No. 8 pp. 5365-5368), describes materials with a large magnetocaloric effect based on Gd and its alloys such as those in the ternary alloy system Gd—Si—Ge (U.S. Pat. No. 6,589,366B1, or U.S. Pat. No. 5,743,095).
Pr and Nd are known for their use in commercial permanent magnet alloys based on the tetragonal 2:14:1 Fe-based ternary compounds (i.e., Nd2Fe14B and Pr2Fe14B) (US2012282130A1). However, they have not been used in a 2:17 alloy such as NdPrFe17, as in the instant invention, nor the magnetocaloric properties were disclosed or measured.
The binary intermetallic compounds R2Fe17 with R=Nd or Pr are collinear ferromagnets with a high saturation magnetization (i.e., 185 and 192 Am2kg−1 at 5 K, respectively), and Curie temperature around room temperature (285±5 and 335±5 K, respectively). The interest to consider them as potential candidates for room-temperature magnetic refrigeration lies in their low rare-earth content (in comparison with other rare-earth containing alloys). Until now, the assessment of their MC properties has been focused on bulk alloys produced by arc melting followed by a prolonged high-temperature thermal annealing (several days in the 1273-1373 K temperature range) and powdered ball-milled nanocrystalline alloys. (Pedro Gorria, José L. Sánchez Llamazares, Pablo Álvarez, María José Pérez, Jorge Sánchez Marcos, Jesús A. Blanco, “Relative cooling power enhancement in magneto-caloric nanostructured Pr2Fe17”, J. Phys D: Appl. Phys., Vol. 41 (2008) 192003; Pedro Gorria, Pablo Álvarez, Jorge Sánchez Marcos, José L. Sánchez Llamazares, María J. Pérez, Jesús A. Blanco, “Crystal structure, magnetocaloric effect and magnetovolume anomalies in nanostructured Pr2Fe17”, Acta Materialia, Vol. 57 (2009) 1724-1733; Pablo Álvarez, Pedro Gorria, Victorino Franco, Jorge Sánchez Marcos, María José Pérez, José L. Sánchez Llamazares, Inés Puentes Orench, Jesús A. Blanco, “Nanocrystalline Nd2Fe17 synthesized by high-energy ball milling: crystal structure, microstructure and magnetic properties”, J. Phys.: Condens. Matter Vol. 22 (2010) 216005.) Also, in nanometer-sized R2Fe17 (R=Nd or Pr) powders produced by severe mechanical milling of single-phase bulk alloys, a moderate decrease in |ΔSMpeak| together with the enlargement of both δTFWHM and RC has been observed (see three above references).
In the present invention, a magnetocaloric material comprising NdPrFe17 melt spun ribbons is described. The resulting MC properties are compared with those reported for the bulk parent compound Pr2Fe17 to emphasize on the improved refrigerant capacity and working temperature range of the fabricated allow ribbons.